Nozzle for arc heating devices



Oct. 8, 1963 R. c. ESCHENBACH ETAL 3,106,634

NOZZLE FOR ARC HEATING DEVICES Filed April 21, 1961 AIR WATER INVENTORS RICHARD C. ESCHENBACH ROBERT J. WICKHAM GEORGE M. SKINNER Wag/n gram 5r United States Patent NGZZLE FOR ARQ HEATENG DEVICES Richard C. Esclienbach, Indianapolis, Robert J. Wickham,

Plainfield, and George M. Skinner, Indianapolis, Ind.,

assignors to Union Carbide Corporation, a corporation of New York Filed Apr. 21, 19m, Ser. No. 104,577 4 Claims. (Cl. 219-45) This invention relates to improved are heating devices and more particularly to an improved nozzle structure for such are heating devices.

There is an increasing need in industry for apparatus that will produce environmental conditions for certain research and tests on a scaled down or laboratory basis. In certain instances, such conditions have been virtually non-reproduceable on such a laboratory basis. In the aviation, missile and space exploration fields, for example, equipment is desired which will produce gas velocities far exceeding the speed of sound and/or temperatures far exceeding the melting points of most known materials. Devices capable of producing such gas velocities and temperatures on a laboratory basis are largely unattainable. The advantages to be gained from such a device are obvious in terms of making itpossible to pretest airframe shapes, material durability at elevated temperatures and the like. Such pretesting is, of course necessary to the protection of human life and the successful operation and recovery of extremely expensive unmanned vehicles.

High velocity, high temperature air streams are desired for wind tunnels and other materials testing devices. In such devices high gas velocities and temperatures are required.

Electric arcs are essentially high temperature devices and have been used for many years as cutting torches, for plating processes, for cracking hydrocarbons in the production of acetylene, and other similar uses. Of recent years these arc devices have become useful in various high temperature gas heating applications. In such appl-ications, it is of prime importance to supply a maximum amount of power to the arc and then to transfer such power to the gas efiluent. It has been found that if higher power to an arc device is achieved solely through current increases, such additional power is used up primarily in heating the electrodes and their cooling fluid streams. Voltage increases, on the other hand, are substantially completely transmitted as higher heat to the arc gas.

In high power are heating devices, erosion of the electrodes is a major problem. This is especially true of the nozzle electrode wherein the arc of the device terminates. The problem becomes particularly acute when higher current levels, 400 amperes or more, are needed to obtain higher power levels since as the current increases, the current density of the nozzle electrode will also increase up to a point where the electrode material begins to melt. One method of minimizing erosion of the nozzle electrode is to increase the current carrying capacity of the electrode by spreading out or rotating the are around the inner surface of the nozzle. This in effect increases the arc area so as to permit greater overall currents with nominal workable current densities. An effective method of rotating the arc is to place a field coil around the nozzle. However, in order for the coil to eilectively rotate the arc, the inside diameter of the nozzle must be properly chosen. If the mean axial velocity of the gas immediately downstream from the arc termination area is greater than about 2000 ft./sec. the magnetic field required to rotate the arc might be unpractically large. By measuring the velocity immediately downstream of the arc termination area, the velocity of heated gas is being measured. For fixed gas flow rates and power, the velocity increases as the nozzle diameter decreases. For example, at 1000 c.f.h. and kw., the velocity will exceed 2000 ft/sec. for nozzles having inside diameters of less than /2 inch. It is apparent, therefore, that a larger nozzle is needed to more effectively utilize the field coil.

However, to increase the inside diameter of the nozzle poses the problem of maintaining a stable arc at high power levels within the nozzle under varying conditions of gas flows and pressures.

Accordingly, it is the main object of the present invention to provide an improved nozzle electrode capable of handling large amounts of current without damage to the electrode.

Further objects are: To provide a nozzle electrode of sufiicient diameter which in conjunction with a field coil permits the handling of increased amounts of current; to provide a nozzle electrode configuration which maintains a stable are at high power levels.

These and other objects of the invention will in part be obvious and in part become apparent from the ensuing description and drawings the sole FIGURE of which is a cross-sectional view of an arc torch gas heating device incorporatingthe improved nozzle electrode or" the invention.

While in the accompanying drawing the novel nozzle electrode and its surrounding field coil are shown as being used in conjunction with an inner electrode structure of the type described in copending application Serial No. 104,576, it is to be understood that other inner electrode structures may be used with the novel nozzle electrode of the present invention.

According to one embodiment of the invention, the improved nozzle structure comprises a straight-walled nozzle having an ID. of from about /2 to 1 /2 inches and an CD. of from 1 to 2% inches, fluid cooling means surrounding the straight-walled nozzle, and a magnetic field coil adjacent the nozzle for rotating and stabilizing an arc Within the straight-walled nozzle. When relatively high outlet velocities are desired a constriction having an ID. of from /8 to /2 inch is preferably positioned at the nozzle outlet.

For maximum arc stability, the magnetic coil should be arranged relative to the nozzle such that the magnetic field within the nozzle is directed toward the nozzle inlet when no outlet constriction is used and toward the nozzle outlet when such constriction is used.

In its broadest aspects, the method of operation of the subject apparatus comprises striking an arc of at least amperes between a cathode and the nozzle anode, passing a gas through the nozzle passage to provide a velocity immediately downstream from the arc termination area of at least 50 ft/sec. at atmospheric pressure, surrounding the nozzle electrode with an electromagnetic means hav ing a magnetomotive force of at least 5 kilo-ampere turns, such means providing a magnetic field parallel to the direction of gas flow so as to rotate and stabilize the are within the nozzle passage.

Referring to the drawing, the apparatus comprises an electrode nozzle it? having a water sleeve 11 both of which are held rigidly into position with a suitable internal electrode body 12 by a nozzle nut 13. Electrode body 12, which is more fully described in US. application Serial No. 104,576 filed April 21, 1961, is provided with gas passage means 22 for supplying a shielding gas down into a gas cup 24 which carries at its front end a cathode 23. Gas cup 24 has passage means for introducing the shielding gas around the cathode 2.3. The electrode body 12 also has passage means for introducing a. gas to be heated into the area of the arc end of the cathode 2d. The gas cup 24 carrying cathode 23 is cooled by providing a cooling medium through a bore 51 in the body 12 to the cup 24 and then out through tube 30. Nozzle -10 is of a circular cross-section having parallel walls. The magnetic field from coil 14 rotates and stabilizes the arc that is finally established within the nozzle. The coil may be cooled by any suitable means with water cooling being preferred. For maximum efiiciency, the coil should be tightly wound around the nozzle. Power for the coil may be supplied from the same source as that of the torch or it may have a separate supply of its own.

Diverging and converging nozzles have been found to be substantially less efficient at the desired operating conditions.

At power levels of about 100 kw. or more the internal diameter of the nozzle must be in the order of from /2 to 1 /2 inches in order that the arc may be effectively rotated by the field coil. The increased cross-sectional area will, however, result in low (in the order of 100 to 300 tt./sec.) gas velocities within the torch. Under such conditions, the arc will tend to locate at the entrance of the nozzle rather than within the nozzle itself. Such an arc will not only be unstable, but its shorter length will tend to reduce the ac voltage which would mean that less power would be getting to the gas. Further, a mass flow rate of gas in the order of 1000 c.f.h. which is a typical flow rate used in practice in nozzles of the size described would tend to extend the are out beyond the nozzle exit and localize it somewhere on the end of the torch body.

The field coil not only will rotate and spread the are around the internal surface of the nozzle, but it will also, given sufficient field strength, tend to stabilize the are within the central portion of the nozzle. When the gas fiow mate is at the practical level (1000 c. f.h.) and its velocity immediately downstream from the arc termination area is in the order of 200 ft./ sec. at a pressure of one atmosphere, the magnetomotive force of the field coil must be at tleast 10 kilo-ampere turns with its field direction toward the nozzle entrance in order to properly stabilize the arc. There may be occasions, however, when the velocity will be as low as 50 ft./ sec. In such cases, the magnetomotive force required would be at least kilo-arnpere turns.

In many instances the velocity of the gas within the nozzle is not of sufiicient magnitude to be useful for wind tunnels or other high temperature, high velocity testing applications. In such instances, a constriction 15 is attached to the nozzle at the nozzle exit. Depending upon the internal diameter of the constriction, a sufficient pressure differential can be built up between the nozzle interior and the nozzle exit 21 to increase the velocity to desired magnitudes. Such pressure build up within the nozzle increases the ditficulty of maintaining a stable arc within the nozzle. Internal diameters of the constriction 15 of from Ms to /2 inches have been found to be suitable to build pressure above 50 p.s.i.a. so as to yield exit velocities from about 2000 to more than 4000 ft/sec. when the gas is discharging to the atmosphere. Under these conditions, and with the same desired flow rates as previously mentioned, the field coil must have a strength of at least 5 kilo-ampere turns per atmosphere of pressure with the direction of the field downstream toward the nozzle exit.

It is to be noted that the direction of the field when using the constriction is opposite that of using no constriction. This is because in the case of no constriction the gas flow tends to extend the arc out the nozzle exit, while in the other the pressure tends to push the arc back toward the nozzle entrance. The magnetic stabilizer field tends to counteract these tendencies.

The nozzle is kept from melting during operation by water cooling. The water enters the annulus 16 from inlet 17 through annulus 18 and then flows out the outlet 19 by way of annulus 20*. When the internal diameter of the nozzle is 1 inch, the -O.D.-to-I.D. ratio of the nozzle should be between 1.2 and 1.5 in order to provide maximum cooling and prevent melting of the nozzle interior.

The following two examples illustrate the use of the nozzle. In example one, except for the constriction, apparatus of the type depicted in the accompanying drawing was used. In example two the constriction was used.

Example I In this run the nozzle had a 1 inch ID. The magnetic field was supplied by a wateracooled field coil having a magnetomotive force of 10.5 kilo-ampere turns, the direction of the field being toward the nozzle entrance. Air and argon (shielding gas) were supplied to the device at rates or" 990 c.f.h. and 220 c.f.h. respectively yielding a pressure of about 5 p.s.i.g. With the nozzle acting as the anode, 400 amperes was supplied to the device. Under these conditions, the total power developed was 62 kw. or which 48 kw. (77% efiiciency) went to the gas yielding an arc voltage of v. The enthalpy of the gas was 1800' Btu/lb. and it had a calculated exit velocity of 600 it./ sec.

Example 11 In this run the nozzle had a 1 inch ID. A constriction having a inch ID. was placed at the nozzle exit. The field was supplied from a water cooled field coil having a magnetomotive force of 45 kilo-ampere turns, the direction of the field being toward the nozzle exit. Air and argon were supplied to the device at rates of 1470 c.f.h. and 330 c.t.h. respectively. The pressure within the nozzle passage was 38 p.s.i.g. With the nozzle acting as the anode, 400 amperes was supplied to the device. Under these conditions, the total power developed was 76 kW. of which 54 kw. (71% etficiency) went to the gas yielding an arc voltage of v. The enthalpy of the gas was 1400 B.t.u./lb. and it had a calculated exit velocity of 5600 ft./ sec.

Prior art nozzles operated under conditions similar to those in the above examples showed evidence of erosion after only a few minutes so that such nozzles could be used efiiciently only for several mnutes and at most only about 10 minutes. In marked contrast under the conditions given in the above examples the improved nozzle structure of the invention had an accumulative running time or over an hour. Thus it can be seen that the nozzle structure of the invention has a useable life which is approximately 10 times longer than what has heretofore been used in heating devices of the type described.

What is claimed is:

1. In an arc heating device capable of operating at high power and current levels which includes in combination i3. stick cathode having an arc end; means for delivering a protective inert gas to the area of said are end of said stick cathode; a nozzle anode; means for delivering gas under pressure to said nozzle; and means for striking a high pressure arc between said nozzle anode and the arc end of said cathode for heating the gas discharged by said nozzle; the improvement which comprises providing said nozzle with a gas outlet having a straight'walled passage with an inside diameter in the range of from about /2 to about 1 /2 inches; means surrounding said straight-walled passage for establishing a magentic field such means having a magnetomotive force of at least 5 kilo-ampere turns parallel to the direction of gas flow in said nozzle passage for rotating and stabilizing said high pressure arc.

-2. Apparatus according to claim 1 wherein a constricting member having an inside diameter of fi-om about A; to /2 inches is positioned at the outlet of said nozzle; and said magnetic means has a magnetomotive force of at ieast 5 kilo-ampere turns and the magnetic field established thereby is directed toward the nozzle outlet.

3. A method for heating gases which comprises estaiblishing an arc of at least 150 amperes between a cathode and a nozzle anode, passing a stream of gas past the arc end of said cathode, flowing such stream through said nozzle anode at a velocity of in the order of about 50 ft./sec., and surrounding the nozzle anode With a coil having a magnetomotive force of at least 5 kilo-ampere tunns, the resulting field being parallel to the direction of gas flow so as to rotate said are around the nozzle anode.

4. A method for heating gases which comprises establishing an arc of at least 150 amperes between a cathode and a nozzle anode, passing a stream of gas past the arc end of said cathode, flowing such stream through said nozzle anode at a velocity in the order of about 200 ft./sec., and surrounding the nozzle anode with a coil having a magnetomotive force of at least 10 kiloampere turns, the resulting field ibeing parallel to the direction of gas flow so as to rotate said arc around the nozzle anode.

References Cited in the file of this patent UNITED STATES PATENTS 2,945,119 Bl-acklman July 12, 1960 

1. IN AN ARC HEATING DEVICE CAPABLE OF OPERATING AT HIGH POWER AND CURRENT LEVELS WHICH INCLUDES IN COMBINATION A STICK CATHODE HAVING AN ARC END; MEANS FOR DELIVERING A PROTECTIVE INERT GAS TO THE AREA OF SAID ARC END OF SAID STICK CATHODE; A NOZZLE ANODE; MEANS FOR DELIVERING GAS UNDER PRESSURE TO SAID NOZZLE; AND MEANS FOR STRIKING A HIGH PRESSURE ARC BETWEEN SAID NOZZLE ANODE AND THE ARC END OF SAID CATHODE FOR HEATING THE GAS DISCHARGED BY SAID NOZZLE; THE IMPROVEMENT WHICH COMPRISES PROVIDING SAID NOZZLE WITH A GAS OUTLET HAVING A STRAIGHT-WALLED PASSAGE WITH AN INSIDE DIAMETER IN THE RANGE OF FROM ABOUT 1/2 TO ABOUT 1 1/2 INCHES; MEANS SURROUNDING SAID STRAIGHT-WALLED PASSAGE FOR ESTABLISHING A MAGNETIC FIELD SUCH MEANS HAVING A MAGNETOMOTIVE FORCE OF AT LEAST 5 KILO-AMPERE TURNS PARALLEL TO THE DIRECTION OF GAS FLOW IN SAID NOZZLE PASSAGE FOR ROTATING AND STABILIZING SAID HIGH PRESSURE ARC. 